(1) Field of the Invention
This invention relates to a moving target identifying system wherein individual information about moving targets is specified in a base station radar unit, comprising a base station radar unit and mobile station radar units installed in the moving targets. More specifically, it relates to a base station radar unit and mobile station radar unit used in such a system.
(2) Description of the Related Art
One type of system used to identify moving targets is a vehicle ID radar system. FIG. 29 is a drawing showing the concept of such a vehicle ID radar system comprising a base station radar unit 1 installed on a road or at a toll point, and a vehicle radar unit 3 mounted on the number plate of a vehicle.
FIG. 30 is a schematic diagram of the conventional base station radar unit 1 used in the vehicle ID radar system of FIG. 29. The base station radar unit 1 of FIG. 30 uses secondary radar.
FIG. 30 shows an oscillator 11 that generates a transmitting reference signal, a modulator 12 that modulates the transmitting reference signal based on the output of a question code generator 13, a transmitter 14 that generates a transmitted signal based on the output of the modulator 12, and a transmitting antenna 16a that radiates this transmitting signal to the vehicle-mounted radar unit 3.
The figure also shows a receiving antenna 16b that receives a signal from the vehicle-mounted radar unit 3, a receiver 17 that processes signals received from the vehicle-mounted radar unit 3, a response code demodulator 18 that demodulates a response code from the vehicle-mounted radar unit 3 output by the receiver 17, a response code decoder 19 that decodes the response code based on a vehicle data base 20, a display unit 21 that displays the decoded result of the response code decoder 19, and a communications interface 22 for transferring the decoded result of the response code decoder 19 outside the station. Data showing the relationships between vehicles and response codes used in identifying vehicles is stored in the vehicle data base 20.
FIG. 31 is a schematic diagram of the conventional vehicle-mounted radar unit 3 in the vehicle ID radar system shown in FIG. 29.
In FIG. 31, an oscillator 31, modulator 32, transmitter 34, transmitting antenna 36a, receiving antenna 36b and receiver 37 respectively correspond to the oscillator 11, modulator 12, transmitter 14, transmitting antenna 16a, receiving antenna 16b and receiver 17 of the base station radar unit 1, and have identical functions to them.
In addition, the vehicle-mounted radar unit 3 comprises a question code demodulator 28 that demodulates question codes contained in the signal transmitted by the base station radar unit 1, and a response code generator 41 that generates response codes based on the demodulated question codes.
FIG. 32 is a diagram showing the question and answer exchange that takes place between the base station radar unit 3 and vehicle-mounted radar unit 3.
In a conventional vehicle ID data system, the base station radar unit 1 may for example be installed near a toll point on a toll road, issuing predetermined questions to vehicles that pass through the point, identifying the vehicles and performing tariffing by decoding the responses to these questions. The vehicle-mounted radar unit 3 in this vehicle ID radar system, on the other hand, generates predetermined responses to the questions from the base station radar unit 1, and returns them to the base station. Due to the nature of this question and answer exchange, this vehicle ID radar system is a type of secondary radar.
The action of the base station radar unit 1 will now be described in detail with reference to FIG. 30.
The question code generator 13 generates question codes continuously, or when it is detected that a vehicle is near, it generates a code for that vehicle. This question code is modulated in the modulator 12, and transmitted to the vehicle-mounted radar unit 3 via the transmitter 14 and transmitting antenna 16a.
In response to the transmitted question code, the vehicle-mounted radar unit 3 returns a predetermined response code. The action of the vehicle-mounted radar unit 3 will be described hereinafter. The signal transmitted by the vehicle-mounted radar unit 3 is received by the receiving antenna 16b and input to the receiver 17. The response code demodulator 18 demodulates the response code based on the output of the receiver 17.
The response code decoder 19 decodes the demodulated response code and generates an address signal to read the vehicle data base 20.
Based on this address signal, the response code decoder 19 reads corresponding vehicle information. The processing result of the response code decoder 19 is displayed on the display unit 21, and output to the communications interface 22 to perform communication with other equipment.
Next, the vehicle-mounted radar unit 3 will be described in detail with reference to FIG. 31.
The signal related to question codes radiated by the base station radar unit 1, is received by the receiving antenna 36b and input to the receiver 37. A question code demodulator 38 demodulates the question code based on the output of the receiver 37.
The response code generator 41 generates a response as a response code corresponding to the nature of the question specified by the question code output by the question code demodulator 38.
This response code is input to the modulator 32 and modulated. Subsequently, it is transmitted to the base station radar unit 1 via the transmitter 34 and transmitting antenna 36a.
A typical question and response sequence is shown in FIG. 32. This figure shows the case of a question "What is your ID?", to which for example the response "Yokohama 77-1234" is obtained.
This conventional vehicle ID radar system can therefore identify vehicles.
However, in the aforesaid conventional vehicle ID radar system, only one response code is returned from the vehicle-mounted radar unit 3. The base station radar unit 1 therefore could not obtain other information from the vehicle, for example information about its speed or position, whether the vehicle battery is functioning, or whether or not the vehicle-mounted radar unit is functioning properly.
It may also occur that the response code generator 41 of the vehicle-mounted radar unit 3 has been modified so that a correct response code cannot be obtained. In this case, toll road and other systems using this vehicle ID radar system may not function correctly.